All facets of the sport? Khabib pulled out of a lot fights. It got so bad that during the last 7 years of his career, he only managed to make it to the cage 8 times.
When the fight with Tony Ferguson became a reality at UFC 209, Khabib couldn't make weight and took the cowardly way out by not telling anybody in the UFC. Instead, he just no-showed the weigh-ins and scurried off to a random hospital, where the ER doctors determined that there was nothing wrong with Khabib. He was simply dehydrated and wasting their time, so he was discharged after receiving an IV.
Prior to the UFC, Khabib was a welterweight. He struggled to make 155 throughout his career in the UFC. It got to the point where Khabib could only make weight on an Abu Dhabi scale with their generous weigh-in technique.